1. Technical Field
The present invention relates to a driving circuit for driving a capacitive load.
2. Related Art
As an ink jet printer that discharges an ink and prints an image or a document, a printer that uses piezoelectric elements (for example, piezo elements) is known. The piezoelectric elements are provided respectively corresponding to a plurality of nozzles in a head unit and are respectively driven in response to drive signals and thereby, a predetermined amount of an ink (liquid) is discharged from the nozzle at a predetermined timing such that a dot is formed. The piezoelectric element is a capacitive load like a capacitor in terms of electric power. Therefore, a sufficient current supply is required to operate the piezoelectric elements of the nozzles.
Therefore, a configuration is employed, in which a drive signal amplified by using an amplifier circuit is supplied to a head unit such that the piezoelectric element is driven. Examples of the amplifier circuit include an amplifier circuit having a system of performing current amplification of a source signal before amplification through class AB amplification or the like. However, since the system is poor in energy efficiency, class D amplification has been proposed recently (see JP-A-2010-114711).
In order to stabilize a frequency of self-oscillation in such class D amplification, a technique in which a phase locked loop (PLL) is provided in a feedback path for the self-oscillation such that a frequency of a signal of the self-oscillation is caused to approximate to a frequency of a reference signal has been proposed (see JP-A-2013-118628).
Incidentally, in the configuration in which the PLL is provided in the feedback path (loop) of the self-oscillation, an oscillation circuit for generating the reference signal is separately required, which results in complication of the circuit.